import re
import tkinter
import tkinter.messagebox

root = tkinter.Tk()
#设置窗口大小和位置
root.geometry('300x270+400+100')
#不允许改变窗口大小
root.resizable(False,False)
#设置窗口标题
root.title('简易计算机-曾彦婷')

#放置用来显示信息的文本框，并设置为只读
contentVar=tkinter.StringVar(root,'')
contentEntry=tkinter.Entry(root,textvariable=contentVar)
contentEntry['state']='readonly'
contentEntry.place(x=10,y=10,width=280,height=20)

#按钮通用代码，参数btn表示按钮是哪个按钮
def buttonClick(btn):
    content = contentVar.get()
    #如果已有内容是以小数点开头的，前面加0
    if content.startswith('.'):
        content = '0' + content

    #根据不同按钮做出相应的处理
    if btn in '0123456789':
        content += btn
    elif btn == '.':
        #如果最后一个运算数中已经有小数点，就提示错误
        lastPart = re.split(r'\+|-|\*|/]',content)[-1]
        if '.' in lastPart:
            tkinter.messagebox.showerror('错误','小数点太多了')
            return
        else:
            content += btn
    elif btn == 'C':
        #清除整个表达式
        content = ''
    elif btn =='=':
        try:
            #对输入的表达式求值
            content = str(eval(content))
        except:
            tkinter.messagebox.showerror('错误','表达式有误')
            return
    elif btn in operators:
        if content.endswith(operators):
            tkinter.messagebox.showerror('错误','不允许存在连续运算符')
            return
        content += btn
    elif btn == 'Sqrt':
        n = content.Split('.')
        if all(map(lambda x:x,isdigit(),n)):
            content = eval(content)**0.5
        else:
            tkinter.messagebox.showerror('错误','表达式错误')
            return

    contentVar.set(content)

#放置清除按钮和等号按钮
btnClear = tkinter.Button(root,text='Clear',command=lambda: buttonClick('C'))
btnClear.place(x=40,y=40,width=80,height=20)
btnCompute = tkinter.Button(root,text='=',command=lambda: buttonClick('='))
btnCompute.place(x=170,y=40,width=80,height=20)

#放置10个数字，小数点和计算平方根的按钮
digits = list('0123456789.')+['Sqrt']
index = 0
for row in range(4):
    for col in range(3):
        d = digits[index]
        index += 1
        btnDigit = tkinter.Button(root,text=d,command=lambda x=d: buttonClick(x))
        btnDigit.place(x=20+col*70,y=80+row*50,width=50,height=20)
#放置运算符按钮
operators = ('+','-','*','/','**','//')
for index,operator in enumerate(operators):
    btnOperator = tkinter.Button(root,text=operator,command=lambda x=operator:buttonClick(x))
    btnOperator.place(x=230,y=80+index*30,width=50,height=20)

root.mainloop()